Tsunami evacuation risk change associated with urban recovery in Banda Aceh after 2004 Aceh tsunami

Twenty years after the 2004 Aceh tsunami, Banda Aceh has undergone significant urban recovery, including the development of tsunami evacuation infrastructure. However, shifts in population distribution and evacuation capacity necessitate a reassessment of tsunami evacuation risk. This study evaluates the extent to which the “Build Back Better” strategy has been realized in terms of tsunami evacuation risk reduction, considering long-term population changes and the expansion of evacuation facilities. Using WorldPop Hub data (2000–2020), we analyzed demographic changes within tsunami risk zones in Banda Aceh. While the highest-risk zone (R3) experienced a population reduction to three-quarters of its previous level, the risk-free zone (R0) saw a 6.9 percentage point increase, suggesting relocation from high-risk coastal areas. However, nearly 29 % of Banda Aceh's population still resides in high-risk zones, highlighting persistent vulnerabilities. To assess evacuation feasibility, we conducted network-based tsunami evacuation simulations in Meuraxa, the most at-risk district, under three scenarios: (A) horizontal evacuation only, (B) using existing tsunami evacuation buildings (TEBs), and (C) using both TEBs and nearby facilities. The evacuation failure rates within the 35-min tsunami arrival time were 84.5 %, 3.1 %, and 1.1 %, respectively, indicating the remaining risks despite recovery efforts. While TEBs reduced evacuation times by over 30 min, facility capacity remained imbalanced, with some exceeding capacity tenfold. These findings highlight the need for improved evacuation facility placement and capacity to enhance future tsunami resilience.